Which of the following is an example of a first-class lever?

A first-class lever is defined by its arrangement of the fulcrum, effort, and load. In a first-class lever, the fulcrum is positioned between the effort (the force applied) and the load (the weight being moved). This configuration allows the lever to change the direction of the applied force and can provide a mechanical advantage.

In the case of a seesaw, the fulcrum is located in the center, with the effort applied at one end and the load (the weight of a person) at the opposite end. This setup exemplifies how first-class levers can be used to lift weights on one side by pushing down on the other, thus enabling balanced motion and efficient force distribution.

The other options, such as tweezers, scissors, and crowbars, represent different types of levers. Tweezers and scissors are classified as third-class levers because the effort is applied between the fulcrum and the load, while a crowbar is considered a second-class lever, where the load is between the fulcrum and the effort. Understanding the arrangement of the fulcrum, effort, and load is crucial in identifying the type of lever being described.